Typical color display systems include a display device such as a cathode ray tube having three-color inputs, for example, for providing the primary colors of blue, red, and green, respectively. If electrical signals representing three different images, for example, are connected respectively to the red, green, and blue input terminals of the display device, wherever the images overlap on the display, the associated color images will "mix". If for example a green colored image overlaps with a red colored image at a given location or locations on a display, a yellow coloration will result wherever such overlap occurs.
In Krause et al. U.S. Pat. No. 4,574,277, a computer-controlled video display system is disclosed which includes three video memory planes, each associated with an individual primary color, and each of which may be selectively disabled for obtaining special effects. One special effect is that of providing limited animation by displaying one page while generating a new page in a non-display page. Krause et al. disables a currently displayed plane while enabling a new plane, thereby providing instantaneous page modification for simulating various animations. Three banks of memory are included for producing either eight colors or eight levels of grey-scale display. A RAM memory is used for storing bit-map videographics from a computer implemented for driving the video display. As previously mentioned, selective disablement of any of the eight video planes is used to obtain a desired effect.
Mossaides U.S. Pat No. 4,509,043 discloses a system for superimposing either monochrome or multicolor images on a display to form a composite image. The various images are prioritized via operator selection, and the prioritized data is stored in a memory. An arithmetic logic unit is used to control the brightness of each image in accordance with its priority, for making the highest priority image have the greatest brightness at points of intersection of the various images.
In Brown et al. U.S. Pat. No. 4,484,187, interactive color addressing is used to provide a video display of overlying images. Two memories are used to store pixel data relating to the two images, which data is then multiplexed and provided to a color-map memory. The color-map memory is organized to provide image priority. Portions of each image are provided to the various color guns in accordance with the priorities established in order to provide multicolor images in an overlying manner on the display.
Raman U.S. Pat. No. 4,420,770 teaches a system for generating video background information. Up to sixteen images are stored in a memory. A priority encoder is included to prioritize the pixel information of each image at a given pixel location to control the area and type of background that are to appear in the output video.
U.S. Pat. No. 4,554,538 teaches a raster scan display system for overlapping images in a multicolor display system, wherein non-interfering erasure and relocation of pixels for one image relative to another is provided by a method for incrementing or decrementing, by one count, the address of the particular pixel. In this manner, interference is substantially eliminated between the overlapping images.